Molecular scaffolds for HIV-1 immunogens

ABSTRACT

Methods and compositions are provided which employ chimeric polypeptides having at least one heterologous epitope for a human immunodeficiency virus type 1 (HIV-1) neutralizing antibody. These chimeric polypeptides behave as molecular scaffolds which are capable of presenting the various heterologous HIV-1 epitopes. The invention demonstrates that a heterologous epitope recognized by the HIV-1 neutralizing antibody can be more fully exposed to neutralizing antibodies when presented within the backbone of the chimeric polypeptide than when the epitope is presented within the context of an HIV-1 backbone. Polynucleotides encoding these chimeric polypeptides are also provided. Immunogenic compositions are provided which comprise a chimeric polypeptide having at least one heterologous epitope that interacts with an HIV-1 neutralizing antibody. Immuno genie compositions comprising chimeric polynucleotides encoding the chimeric polypeptides of the invention are also provided. Vaccines comprising such immunogenic compositions are also provided. Further provided are methods which employ the immunogenic compositions of the invention. Such methods include, for example, methods for eliciting an immune response in a subject, methods for generating antibodies specific for the chimeric polypeptide or the chimeric polypeptide, and methods for inhibiting or preventing infection by HIV-1 in a subject.

FIELD OF THE INVENTION

The invention relates to the field of retroviruses, particularly lentivirus.

BACKGROUND OF THE INVENTION

Broadly neutralizing antibodies to HIV will likely be needed if any AIDS vaccine is to prevent people from becoming infected with HIV. Most of the AIDS vaccine candidates now entering clinical trials are aimed at stimulating certain infection-fighting white blood cells, not antibodies. While these vaccines may prevent people who become infected with HIV from progressing to AIDS, they are not likely to prevent an infection in the first place. To do that, neutralizing antibodies against HIV-1 will likely be needed as well.

Given the potential anti-viral effects of neutralizing antibodies, it is not unexpected that HIV-1 has evolved multiple mechanisms to protect it from antibody binding including, for example, the heavy glycosylation of the envelope polypeptide, the trimerization of the gp120 and gp41 structure which can shield antibody access to the underlying peptide structure, and the kinetics and spatial constraints that impede antibodies from binding potentially vulnerable sites during receptor binding and membrane fusion. However, despite all of the defense mechanisms of HIV against neutralizing antibodies, primary isolates of HIV from different genetic subtypes can be neutralized by some broadly reactive human monoclonal antibodies such as b12, 2G12, 2F5, Z13, and 4E10. In addition, a few rare sera from HIV-1 infected individuals have broad neutralizing activity. The existence of such broadly neutralizing antibodies provides an indication that a vaccine inducing neutralizing antibodies can indeed be created.

Methods and compositions are needed in the art which provide immunogens that elicit neutralizing antibodies against HIV-1.

BRIEF SUMMARY OF THE INVENTION

An immunogenic composition is provided which comprises a chimeric envelope polypeptide or a functional variant thereof wherein the envelope polypeptide is from a lentivirus that is not HIV-1, and the chimeric envelope polypeptide comprises at least one heterologous epitope recognized by an HIV-1 neutralizing antibody. In specific embodiments, the envelope polypeptide is selected from the group consisting of an HIV-2 envelope polypeptide, a functional variant of the HIV-2 envelope, a Simian Immunodeficiency virus (SIV) envelope polypeptide or a functional variant of the SIV envelope polypeptide. In other embodiments, the heterologous epitope is derived from an HIV-1 envelope polypeptide.

Also provided is an immunogenic composition comprising a polynucleotide encoding a chimeric envelope polypeptide or a functional variant thereof that is not from HIV-1. The polypeptide encoded by the polynucleotide further comprises at least one heterologous epitope that is recognized by an HIV-1 neutralizing antibody. In specific embodiments, a nucleotide sequence encoding the chimeric envelope polypeptide encodes an HIV-2 envelope polypeptide, a functional variant of the HIV-2 envelope polypeptide, a Simian Immunodeficiency virus (SIV) envelope polypeptide, or a functional variant of the SIV envelope polypeptide. In specific embodiments, the heterologous epitope is derived from an HIV-1 envelope polypeptide.

In further compositions, the heterologous epitope recognized by the HIV-1 neutralizing antibody is from the gp41 polypeptide, the gp120 polypeptide, the membrane proximal external region of gp41, or the variable loop region of gp120. In still other compositions, the heterologous epitope comprises a 4E10 epitope, a Z13 epitope, or a 2F5 epitope.

The immunogenic compositions of the invention can further comprise a pharmaceutically acceptable carrier, diluent, or adjuvant. In addition, in specific embodiments, the immunogenic composition comprises a vaccine.

A method for eliciting an immune response in a subject is provided. The method comprises introducing into a subject an effective concentration of the immunogenic composition of the invention. Further provided is a method for generating antibodies specific for a chimeric polypeptide of the invention. The method comprises introducing into a subject an effective concentration of an immunogenic composition of the invention. Additional methods are provided for inhibiting or preventing infection by HIV-1 in a subject. Such a method comprises administering to the subject an effective amount of an immunogenic composition of the invention.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 shows the envelope gp120 alignments for HIV-2 (7312A (SEQ ID NO:2) and UC1 (SEQ ID NO:7)), SIV (Mac239 (SEQ ID NO:11) and Ver-TyO1 (SEQ ID NO:12)), and HIV-1 (YU2 (SEQ ID NO:13) and HXB2 (SEQ ID NO:10)). Bridging sheet, variable loops, amino acid identities, and site-directed mutations (H419R, Q422L, and V434M) are indicated. The signal peptide-gp120 cleavage position for HIV-1 is shown. Variable loops (V1/V2, V3, and V4) have conventionally been defined by disulfide-linked cysteine residues at their bases, as depicted. However, the actual limits of variable loops have been resolved structurally in the HXB2-CD4-17b crystal complex (Kwong (1998) Nature 393:648-659), and these sequences are indicated by green bars. It is possible that structural details diverge in the more distantly related HIV/SIV sequences. The amino acids contributing to the bridging sheet are highlighted. Circles indicate residues contributing to chemokine co-receptor binding based on site-directed mutagenesis studies (Rizzuto (1998) Science 280:1949-1953; Rizzuto (2000) AIDS Res Hum Retroviruses 16:741-749). Additional amino acids within the stem of V3, including 298R, 301N, 303T, 3231, 325N, 326M and 327R, may contribute to gp120 interaction with CCR5 (Cormier (2001) J Virol 75:5541-5549). Triangles indicate HIV-1 contact residues for CD4 based on crystal structure analyses (Kwong (1998) Nature 393:648-659). Asterisks below the sequence indicate conservation of amino acid identity across all five virus strains. Overall gp120 sequence identity was calculated based on amino acid residues exclusive of the initiator methionine of the (cleaved) signal peptide and a gap-stripped alignment of the sequences shown. Except for SIVverTYO1, sequences were obtained from the HIV Sequence Compendium 2002 (HIV Sequence Compendium (2002) Kuiken et al. Eds. Los Alamos National Laboratory, Los Alamos, N. Mex., LA-UR 03-3564). We determined experimentally the nucleotide sequence of the SIVverTYO1 clone used in our studies (lambda phage SAH12) and found that it differed from the reported sequence of the same clone in the Compendium at positions 171(−), 172(N), 402(D), 418(C) and 427(W).

FIG. 2 shows the complete sequences for thirty-one gp160 envelope clones of plasma virus from subject SUMA0874 with V3 region indicated. Clones are identified according to the day following onset of symptoms of the acute retroviral syndrome the plasma sample was obtained (e.g., S004-11 refers to clone number 04 from a plasma sample taken 11 days following symptom onset, a point when the patient was viral RNA positive and viral antibody negative by ELISA and immunoblot). A subset of the clones depicted was analyzed previously in a study of neutralizing antibody escape (Wei et al. (2003) Nature 422:307-312). Four additional gp160 sequences depicted correspond to wild-type clones S736-68 and S736-73 that were modified by site-directed mutagenesis to contain substitutions at the 308 or 309 positions. These are designated S736-68 nm/T1, S736-68 m/P1, S736-73 m/TT, and S736-73 m/PI. The critical amino acid substitution at position 309 (isoleucine to threonine) in clones S736-68 and S736-75 responsible for spontaneous co-receptor exposure is highlighted in yellow as is the site-directed mutation made in the wild-type clone S736-73 (S736-73 m/TT).

FIG. 3 provides an alignment of the amino acid sequences of various envelope polypeptides from HIV-2 viruses including, 7312A (SEQ ID NO:2), UC1 (SEQ ID NO:7), UC2 (SEQ ID NO:8) and ROD-D.14 (SEQ ID NO:9) and the amino acid sequence of envelope from HIV-1 virus HXB2 (SEQ ID NO: 10).

FIG. 4 provides the location of 2F5 (single underline) and 4E10 (double underline) Epitopes in HIV-1 (YU-2 and HXB-2) gp41 and corresponding sequences in HIV-2 (ST, 7312A, and UC1). This alignment shows the conservation of the 4E10 epitope at a sequence level and as a target of 4E10-mediated neutralization between HIV-1 and HIV-2. The envelope polypeptides comprises ST (SEQ ID NO:14), 7312A (SEQ ID NO:2); UC1 (SEQ ID NO:7), HXB-2 (SEQ ID NO:10), and YU-2 (SEQ ID NO:13).

FIG. 5 shows the neutralization of HIV-1 by 4E10 monoclonal antibodies. These data show that certain naturally-occurring or genetically-modified strains of HIV-2 can be used to detect HIV neutralization by 4E10 and 4E10-like antibodies.

FIG. 6 provides a 2-D schematic of HXB2 gp41e from HIV Molecular Immunology (2002) Bette et al. eds., Los Alamos National Laboratory, Theoretical Biology and Biophysics, Los Alamos, N. Mex. LA-UR 03-5816. The figure illustrates the position of the 2F5/4E10/Z13 epitope cluster, epitope cluster II, the C-helix, N-helix, and epitope cluster I.

FIG. 7 provides the amino acids sequence of 6 chimeric envelope polypeptides from HIV-2 7312A. Amino acids 648 to 687 of the 7312A envelope polypeptide (SEQ ID NO:2) is shown with a region of the MPER double underlined. The constructs designated as 7312A-C1, 7312A-C2, 7312A-C3, 7312A-C4 (SEQ ID NO:27, 29, 31, and 33, respectively) are chimeric 7312A envelope polypeptides in which a region of the MPER domain from an HIV-1 envelope polypeptide has been substituted for the native HIV-2 sequence. The heterologous domain derived from HIV-1 is in bold and highlighted. Similarly, constructs 7312A-C5 and 7312A-C6 (SEQ ID NO:35 and 37, respectively) represent chimeric 7312A envelope polypeptides in which specific amino acid substitutions were made to introduce HIV-1 epitopes into the HIV-2 envelope polypeptide.

FIG. 8 provides an alignment of the gp41 region of HIV-1 (YU-2) and corresponding sequences in HIV-2 (ST, 7312A, and UC1) highlighting the 2F5 (single underline) and 4E10 (double underline) epitopes within the MPER. The envelope polypeptides comprises ST (SEQ ID NO:14), 7312A (SEQ ID NO:2); UC1 (SEQ ID NO:7), and YU-2 (SEQ ID NO:13).

DETAILED DESCRIPTION OF THE INVENTION

The present inventions now will be described more fully hereinafter with reference to the accompanying examples, in which some, but not all embodiments of the invention are shown. Indeed, these inventions may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout.

Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

The article “a” and “an” are used herein to refer to one or more than one (i.e., to at least one) of the grammatical object of the article. By way of example, “an element” means one or more than one element.

Overview

The membrane proximal external region (MPER) epitopes 4E10 and 2F5, and surrounding peptide sequences, are broadly cross-reactive neutralizing epitopes on HIV-1. However, to date, all studies attempting to use this region of the HIV-1 envelope glycoprotein as an immunogen to elicit neutralizing antibodies have failed (reviewed in Burton et al. (2004) Nature Immunol 5:233-6; Zolla-Pazner et al. (2004) Nature Rev Immunol 4:199-210; Offek et al. (2004) J Virol 78:10724-37; Binley et al. (2004) J Virol 78:13232-52; and, Zwick et al. (2005) J Virol 79:1252-61). The present invention demonstrates that envelope polypeptides from lentiviruses that are not HIV-1 can be successfully employed as molecular scaffolds to present various heterologous epitopes that are recognized by HIV-1 neutralizing antibodies. We demonstrate that the heterologous epitopes in these chimeric polypeptides are more fully exposed to neutralizing antibodies when they are presented within the backbone of the chimeric polypeptide than when the epitope is presented within the context of an HIV-1 backbone. The present invention discloses various compositions and methods which employ these chimeric polypeptides as immunogens which can elicit protective antibodies against HIV.

Compositions

The present invention provides various immunogenic compositions. As used herein an “immunogenic composition” refers to any composition that is capable of eliciting an immune response. The term “vaccine” refers to an immunogenic composition that reduces the risk of, or prevents, infection by an infectious agent (a “prophylactic vaccine”) or that ameliorates, to any extent, an existing infection (a “therapeutic vaccine”). If a vaccine protects an organism from subsequent challenge with the infectious agent, the vaccines is said to be “protective.”

1. Chimeric Envelope Polypeptides and Polynucleotides

The present invention provides an immunogen comprising a chimeric envelope polypeptide which is not from HIV-1 which comprises at least one heterologous epitope that is recognized by an HIV-1 neutralizing antibody. Additional immunogens of the invention include chimeric polynucleotides comprising a nucleotide sequence encoding an envelope polypeptide or a variant thereof, wherein the envelope sequence is not from HIV-1 and wherein the nucleotide sequence further encodes a heterologous epitope recognized by an HIV-1 neutralizing antibody.

As used herein, a “heterologous domain” or “heterologous epitope” comprises a domain that is not present in the native polynucleotide or polypeptide or the domain/epitope is found in an alternative location in the native polynucleotide or polypeptide. For example, a heterologous epitope for an HIV-1 neutralizing antibody comprises an epitope that is not present in the native non-HIV-1 envelope polypeptide (or the polynucleotide encoding the same). Alternatively, the heterologous epitope could comprise an epitope that is found in an alternative location in the native non-HIV-1 envelope polypeptide (or the polynucleotide encoding the same). Polypeptides or polynucleotides comprising such heterologous epitopes are referred to herein as “chimeric polypeptides” or “chimeric polynucleotides”, respectively. Heterologous epitopes which can be employed in the chimeric polypeptides of the invention are discussed elsewhere herein, as are various methods to determine if such an epitope is present in the envelope polypeptide.

In specific embodiments, the chimeric polynucleotides or polypeptides of the invention are isolated or substantially purified polynucleotide or polypeptide compositions. An “isolated” or “purified” polynucleotide or polypeptide, or biologically active portion thereof, is substantially or essentially free from components that normally accompany or interact with the polynucleotide or polypeptide as found in its naturally occurring environment. Thus, an isolated or purified polynucleotide or polypeptide is substantially free of other cellular material, or culture medium when produced by recombinant techniques, or substantially free of chemical precursors or other chemicals when chemically synthesized. Optimally, an “isolated” polynucleotide is free of sequences (optimally protein encoding sequences) that naturally flank the polynucleotide (i.e., sequences located at the 5′ and 3′ ends of the polynucleotide) in the genomic DNA of the organism from which the polynucleotide is derived. For example, in various embodiments, the isolated polynucleotide can contain less than about 5 kb, 4 kb, 3 kb, 2 kb, 1 kb, 0.5 kb, or 0.1 kb of nucleotide sequence that naturally flank the polynucleotide in genomic DNA of the cell from which the polynucleotide is derived. A protein that is substantially free of cellular material includes preparations of protein having less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of contaminating protein. When the polypeptide of the invention or biologically active portion thereof is recombinantly produced, optimally culture medium represents less than about 30%, 20%, 10%, 5%, or 1% (by dry weight) of chemical precursors or non-protein-of-interest chemicals.

The chimeric envelope polypeptide employed in the methods may be either in the glycosylated or deglycosylated form. In addition, the envelope polypeptide of the invention or polynucleotide encoding the same can be an envelope polypeptide from any lentivirus or any primate lentivirus. In specific methods, the envelope polypeptide is from any primate lentivirus that is not HIV-1. Such primate lentivirus include, for example, HIV-2 (Isolate BEN), HIV-2 (Isolate CAM2), HIV-2 (Isolate D194), HIV-2 (Isolate D205,7), HIV-2 (Isolate GHANA-1), HIV-2 (Isolate ROD); Simian AIDS retrovirus (SRV-1) such as, SIV (AGM155), SIV (AGM266 isolate), SIV (AGM3 isolate), SIV (AGM385 isolate), SIV (F236/SMH4 isolate, Sooty Mangabey), SIV (TyO-1 isolate) and SIVagm; Simian immunodeficiency virus, such as, SIV (1A11 isolate), SIV (isolate African mandril), SIV (AGM/clone Gri-1), SIV (vervet), SIV (Tantalus), SIV (STM isolate), SIV (17E-C1), SIV Qu, SIVdeb, SIVmac, SIVMND, SIVmon, SIVsm; Simian immunodeficiency virus 2; and Simian-Human immunodeficiency virus.

In specific embodiments, the envelope polypeptide used to construct the chimeric polypeptide is from HIV-2. For example, in one method, an HIV-2 envelope polypeptide or functional variants thereof is used. By “HIV-2 envelope polypeptide” or “envelope encoded by an HIV-2 polynucleotide” is intended the form of the HIV-2 envelope polypeptide, or polynucleotide encoding the same, in the HIV-2 viral isolate 7312A. The amino acid of the envelope polypeptide of the HIV-2 isolate 7312A is set forth in SEQ ID NO:2. The nucleotide sequence encoding the envelope polypeptide of the HIV-2 isolate 7312A is set forth in SEQ ID NO:21.

Variants of the HIV-2 envelope polypeptide are biologically active, that is they continue to possess the desired biological activity of the native protein, that is, they continue to interact with CD4 and/or facilitate virus fusion and/or facilitate viral entry into a permissive cell. It is further recognized that the viral envelope polypeptide is produced as a precursor (gp 160) that is subsequently cleaved into two parts, gp120 which binds CD4 and chemokine receptors, and gp41, which is anchored in the viral membrane and mediates viral fusion. Variants of the HIV-2 envelope polypeptide encompass fragments of HIV-2 envelope including, for example, gp41, gp120 or any other fragment that retains the necessary activity. The amino acid sequence comprising gp41 and gp120 is denoted in FIGS. 1, 2, 3 and 4. Various domains of the HIV-2 envelope polypeptide include gp41 (about amino acids 513-857 of SEQ ID NO:2) and gp120 (about amino acids 20-514 of SEQ ID NO:2). Additional domains of HIV envelope polypeptides are discussed in further detail in Burton et al. (2004) Nature Immunology 5:233 and Zwick et al. (2004) Nature Medicine 10:133, both of which are herein incorporated by reference.

Variants of HIV-2 envelope polypeptide are known. See, for example, FIGS. 1 and 3 which provide the amino acid sequence of envelope polypeptides from various HIV-2 strains, including UC1, UC2, and ROD-B. Assays to measure HIV-2 envelope activity include, for example, envelope binding assays to CD4 and cell fusion assays. Such methods are described in detail in Martin et al. (2003) Nature Biotechnology 21:71-76, herein incorporated by reference in its entirety.

In other embodiments, the envelope polypeptide used to construct the chimeric polypeptide is an SIV envelope polypeptide or a functional variant thereof. By “SIVsm envelope polypeptide” or “envelope encoded by an SIVsm envelope polynucleotide” is intended the form of the SIVsm envelope polypeptide or polynucleotide encoding the same in SIVsm PBJ1.9. The amino acid of the envelope polypeptide of the SIVsm PBJ1.9 is set forth in SEQ ID NO:3 and the nucleotide sequence encoding this polypeptide is set forth in SEQ ID NO:22. In other methods, a SIVsm envelope polypeptide, polynucleotide, or a functional variant thereof is used to generate the chimeric polypeptide or polynucleotide. See, also, Israel et al. (1993) AIDS Res. Hum. Retroviruses 9:277-286; Hirsch et al. (1998) Nat. Med. 4(12):1401-8; Mahalingam et al. (2001) J. Virol. 75(1):362-74, each of which is herein incorporated by reference.

By “SIVagm envelope polypeptide” or “envelope encoded by an SIVagm polynucleotide” is intended the form of the SIVagm envelope polypeptide or polynucleotide encoding the same in SIVagmVer155. The amino acid sequence of the envelope polypeptide of SIVagmVer155 is set forth in SEQ ID NO:4. See, also, Johnson et al. (1990) J. Virol. 64 (3), 1086-1092, herein incorporated by reference. Other envelope polypeptides from SIVagm are known. For example, the amino acid sequence for the envelope polypeptide from SIVagmTAN is provided in SEQ ID NO:5. See, also, Soares et al. (1997) Virology 228 (2): 394-399.

Variants of the SIV envelope polypeptide are biologically active, that is they continue to possess the desired biological activity of the native protein (i.e., they continue to interact with CD4 and/or facilitate virus fusion and/or facilitate viral entry into a permissive cell). Variants of the SIV envelope polypeptides encompass fragments of SIV envelope including, for example, gp41, gp120 or any other fragment that retains the necessary activity. The amino acid sequences of gp41 and gp120 are denoted in FIGS. 1, 2, 3 and 4.

2. Variant Polynucleotides and Polypeptides

As discussed throughout, the compositions disclosed herein can employ variant envelope polypeptides, variant polynucleotides encoding the envelope polypeptides, as well as variants of the heterologous epitopes recognized by the HIV-1 neutralizing antibodies. As used herein, “variants” is intended to mean substantially similar sequences. A “variant” protein is intended to mean a protein derived from the native protein by deletion (so-called truncation) of one or more amino acids at the N-terminal and/or C-terminal end of the native protein; deletion and/or addition of one or more amino acids at one or more internal sites in the native protein; or substitution of one or more amino acids at one or more sites in the native protein. As used herein, a “native” polynucleotide or polypeptide comprises a naturally occurring nucleotide sequence or amino acid sequence, respectively. As defined herein, the “native” envelope polypeptide of HIV-2 or polynucleotide encoding the same is from the HIV-2 isolate 7312A (SEQ ID NO:2 and 21), the “native” envelope polypeptide of SIVsm or the polynucleotide encoding the same is from SIVsmPBj1.9 (SEQ ID NO:3 and 22), the “native” envelope polypeptide of SIVagm or the polynucleotide encoding the same is from SIVagmVer155 (SEQ ID NO:4 and 23) or SIVagmTAN (SEQ ID NO:5 and 24), and the “native” sCD4 polypeptide is set forth in SEQ ID NO: 1. Variant proteins encompassed by the present invention are biologically active, that is they continue to possess the desired biological activity of the native protein activity as described herein for envelope. Such variants may result from, for example, genetic polymorphism or from human manipulation. Biologically active variants of a native envelope polypeptide and/or a native soluble CD4 polypeptide employed in the methods of the invention will have at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to the amino acid sequence for the native protein as determined by sequence alignment programs and parameters described elsewhere herein. A biologically active variant of a protein of the invention may differ from that protein by as few as 1-15 amino acid residues, as few as 1-10, such as 6-10, as few as 5, as few as 4, 3, 2, or even 1 amino acid residue.

A fragment of a biologically active portion of an envelope polypeptide of the invention will encode at least 15, 25, 30, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 1000, or 1,200 contiguous amino acids, or up to the total number of amino acids present in a full-length envelope polypeptide of the invention.

For polynucleotides, a variant comprises a polynucleotide having deletions (i.e., truncations) at the 5′ and/or 3′ end; deletion and/or addition of one or more nucleotides at one or more internal sites in the native polynucleotide; and/or substitution of one or more nucleotides at one or more sites in the native polynucleotide. As used herein, a “native” polynucleotide or polypeptide comprises a naturally occurring nucleotide sequence or amino acid sequence, respectively. For polynucleotides, conservative variants include those sequences that, because of the degeneracy of the genetic code, encode the amino acid sequence of one of the envelope polypeptides of the invention. Naturally occurring allelic variants such as these can be identified with the use of well-known molecular biology techniques, such as, for example, with polymerase chain reaction (PCR) and hybridization techniques as outlined below. Variant polynucleotides also include synthetically derived polynucleotides, such as those generated, for example, by using site-directed mutagenesis but which still encode an envelope protein of the invention. Generally, variants of a particular polynucleotide of the invention will have at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity to that particular polynucleotide as determined by sequence alignment programs and parameters as described elsewhere herein.

Variants of a particular polynucleotide of the invention (i.e., the reference polynucleotide) can also be evaluated by comparison of the percent sequence identity between the polypeptide encoded by a variant polynucleotide and the polypeptide encoded by the reference polynucleotide. Thus, for example, an isolated polynucleotide that encodes a polypeptide with a given percent sequence identity to the polypeptide of SEQ ID NO:21, 22, 23, or 24 are disclosed. Percent sequence identity between any two polypeptides can be calculated using sequence alignment programs and parameters described elsewhere herein. Where any given pair of polynucleotides of the invention is evaluated by comparison of the percent sequence identity shared by the two polypeptides they encode, the percent sequence identity between the two encoded polypeptides has at least about 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or more sequence identity.

A fragment of an envelope polynucleotide may encode a biologically active portion of an envelope polypeptide. A biologically active portion of an envelope polypeptide can be prepared by isolating a portion of one of the envelope polynucleotides of the invention, expressing the encoded portion of the envelope protein (e.g., by recombinant expression in vitro), and assessing the activity of the portion of the envelope polypeptide. Polynucleotides that are fragments of an envelope nucleotide sequence comprise at least 16, 20, 50, 75, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 800, 900, 1,000, 1,100, 1,200, 1,300, 1,400 or more contiguous nucleotides, or up to the number of nucleotides present in a full-length envelope polynucleotide disclosed herein.

Variant envelope polypeptides of the invention, as well as polynucleotides encoding these variants, are known in the art and are discussed in further detail elsewhere herein. The polypeptide employed in the methods of the invention may be altered in various ways including amino acid substitutions, deletions, truncations, and insertions. Methods for such manipulations are generally known in the art. As discussed below, variant polypeptides or polynucleotides of the invention can comprise heterologous epitopes for HIV-1 binding antibodies. For example, amino acid sequence variants and fragments of the envelope polypeptide can be prepared by mutations in the DNA. Methods for mutagenesis and polynucleotide alterations are well known in the art. See, for example, Kunkel (1985) Proc. Natl. Acad. Sci. USA 82:488-492; Kunkel et al. (1987) Methods in Enzymol. 154:367-382; U.S. Pat. No. 4,873,192; Walker and Gaastra, eds. (1983) Techniques in Molecular Biology (MacMillan Publishing Company, New York) and the references cited therein. Guidance as to appropriate amino acid substitutions that do not affect biological activity of the protein of interest may be found in the model of Dayhoff et al. (1978) Atlas of Protein Sequence and Structure (Natl. Biomed. Res. Found., Washington, D.C.), herein incorporated by reference. Conservative substitutions, such as exchanging one amino acid with another having similar properties, may be optimal.

Thus, the polypeptides and polynucleotides employed in the methods of the invention encompass naturally occurring sequences as well as variations and modified forms thereof. Such variants will continue to possess the desired activity for envelope as discussed elsewhere herein. Obviously, the mutations that will be made in the DNA encoding the variant must not place the sequence out of reading frame and optimally will not create complementary regions that could produce secondary mRNA structure. See, EP Patent Application Publication No. 75,444.

The deletions, insertions, and substitutions of the protein sequences encompassed herein are not expected to produce radical changes in the characteristics of the protein. However, when it is difficult to predict the exact effect of the substitution, deletion, or insertion in advance of doing so, one skilled in the art will appreciate that the effect will be evaluated by routine screening assays. That is, the activity can be evaluated for functional variants of the envelope polypeptides by the ability to interact with CD4 and/or facilitate virus fusion and/or facilitate viral entry into a permissive cell. See, for example, Martin et al. (2003) Nature Biotechnology 21:71-76, herein incorporated by reference.

Methods of alignment of sequences for comparison are well known in the art. Thus, the determination of percent sequence identity between any two sequences can be accomplished using a mathematical algorithm. As used herein, “sequence identity” or “identity” in the context of two polynucleotides or polypeptide sequences makes reference to the residues in the two sequences that are the same when aligned for maximum correspondence over a specified comparison window. When percentage of sequence identity is used in reference to proteins it is recognized that residue positions which are not identical often differ by conservative amino acid substitutions, where amino acid residues are substituted for other amino acid residues with similar chemical properties (e.g., charge or hydrophobicity) and therefore do not change the functional properties of the molecule. When sequences differ in conservative substitutions, the percent sequence identity may be adjusted upwards to correct for the conservative nature of the substitution. Sequences that differ by such conservative substitutions are said to have “sequence similarity” or “similarity”. Means for making this adjustment are well known to those of skill in the art. Typically this involves scoring a conservative substitution as a partial rather than a full mismatch, thereby increasing the percentage sequence identity. Thus, for example, where an identical amino acid is given a score of 1 and a non-conservative substitution is given a score of zero, a conservative substitution is given a score between zero and 1. The scoring of conservative substitutions is calculated, e.g., as implemented in the program PC/GENE (Intelligenetics, Mountain View, Calif.).

As used herein, “percentage of sequence identity” means the value determined by comparing two optimally aligned sequences over a comparison window, wherein the portion of the polynucleotide sequence in the comparison window may comprise additions or deletions (i.e., gaps) as compared to the reference sequence (which does not comprise additions or deletions) for optimal alignment of the two sequences. The percentage is calculated by determining the number of positions at which the identical nucleic acid base or amino acid residue occurs in both sequences to yield the number of matched positions, dividing the number of matched positions by the total number of positions in the window of comparison, and multiplying the result by 100 to yield the percentage of sequence identity.

Unless otherwise stated, sequence identity/similarity values provided herein refer to the value obtained using GAP Version 10 using the following parameters: % identity and % similarity for a nucleotide sequence using GAP Weight of 50 and Length Weight of 3, and the nwsgapdna.cmp scoring matrix; % identity and % similarity for an amino acid sequence using GAP Weight of 8 and Length Weight of 2, and the BLOSUM62 scoring matrix; or any equivalent program thereof. By “equivalent program” is intended any sequence comparison program that, for any two sequences in question, generates an alignment having identical nucleotide or amino acid residue matches and an identical percent sequence identity when compared to the corresponding alignment generated by GAP Version 10.

GAP uses the algorithm of Needleman and Wunsch (1970) J. Mol. Biol. 48:443-453, to find the alignment of two complete sequences that maximizes the number of matches and minimizes the number of gaps. GAP considers all possible alignments and gap positions and creates the alignment with the largest number of matched bases and the fewest gaps. It allows for the provision of a gap creation penalty and a gap extension penalty in units of matched bases. GAP must make a profit of gap creation penalty number of matches for each gap it inserts. If a gap extension penalty greater than zero is chosen, GAP must, in addition, make a profit for each gap inserted of the length of the gap times the gap extension penalty. Default gap creation penalty values and gap extension penalty values in Version 10 of the GCG Wisconsin Genetics Software Package for protein sequences are 8 and 2, respectively. For nucleotide sequences the default gap creation penalty is 50 while the default gap extension penalty is 3. The gap creation and gap extension penalties can be expressed as an integer selected from the group of integers consisting of from 0 to 200. Thus, for example, the gap creation and gap extension penalties can be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or greater.

3. Heterologous Epitopes

As used herein, an “HIV-1 binding antibody” comprises an antibody that specifically interacts with an epitope of HIV-1. An HIV-1 binding antibody that can neutralize a virus is referred to herein as an “HIV-1 neutralizing antibody.” As discussed above, the chimeric envelope polypeptides, and polynucleotides encoding the same, are from a lentivirus that is not HIV-1 and further comprises at least one heterologous epitope that is recognized by an HIV-1 neutralizing antibody.

By “specifically interacts” is intended that the antibody that recognizes the epitope of an HIV-1 envelope polypeptide forms a specific antibody-antigen complex with that epitope (either in an in vitro or in vivo setting) when the epitope is contained in an envelope polypeptide that is not from HIV-1. Thus, the HIV-1 binding antibody binds preferentially to the non-HIV-1 envelope polypeptide comprising the heterologous HIV-1 epitope. By “binds preferentially” is meant that the antibody immunoreacts with (binds) substantially more of the non-HIV-1 envelope polypeptide comprising the HIV-1 epitope than the non-HIV-1 envelope polypeptide lacking the epitope, when both polypeptides are present in an immunoreaction admixture. Substantially more typically indicates at least greater than 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, or greater of the immunoprecipitated material is the non-HIV-1 envelope polypeptide comprising the HIV-1 epitope.

The heterologous epitope can be native to the HIV-1 envelope polypeptide or alternatively, the epitope can be synthetically derived, so long as the epitope continues to be recognized by the HIV-1 neutralizing antibody. In addition, the heterologous epitope or the heterologous domain containing the epitope can be of any length including about 2 to about 7 amino acids, about 5 to about 10 amino acids, about 11 to about 20 amino acids, about 21 to about 30 amino acids, about 31 to about 40 amino acids, about 41 to about 50 amino acids, about 51 to about 60 amino acids, about 61 to about 70 amino acids, about 71 amino acids to about 80 amino acids, about 81 to about 90 amino acids, about 91 to about 100 amino acids, about 101 to about 110 amino acids, or longer.

The heterologous epitope can be placed anywhere in the envelope sequence, as long as the chimeric polypeptide retains the activity of the native envelope polypeptide. In still further embodiments, the amino acid sequence of a non-HIV-1 envelope polypeptide is aligned with the amino acid sequence of an HIV-1 envelope polypeptide. The chimeric polypeptide is then engineered to comprise the necessary amino acid substitutions, deletions and/or additions that result in the heterologous epitope from the HIV-1 polypeptide to be placed in the corresponding region of the non-HIV-1 envelope polypeptide. Determining such corresponding regions between two polypeptides or polynucleotides is routine in the art. See, for example, FIGS. 1, 3, and 4, which provide representative alignments that allow one to determine “corresponding” amino acids for a subset of lentiviruses.

The nucleotide sequence encoding the heterologous epitope or the domain it is contained in can be of any length including about 15 to about 30 nucleotides, about 31 to about 60 nucleotides, about 61 to about 90 nucleotides, about 91 to about 120 nucleotides, about 121 to about 150 nucleotides, about 151 to about 180 nucleotides, about 181 to about 210 nucleotides, about 210 to about 240 nucleotides, about 241 to about 270, about 271 to about 300, about 301 to about 330 nucleotides, or longer. It is recognized that various methods can be employed to generate the chimeric polynucleotide having the heterologous epitope including nucleic acid substitutions, deletions, truncations, and insertions. Methods for such manipulations are generally known in the art.

Assays to measure envelope activity include, for example, envelope binding assays to CD4, cell fusion assays, and virus entry assays. Such assays are discussed in further detail elsewhere herein. It is recognized that various methods can be employed to generate the chimeric polypeptide having the heterologous epitope including amino acid substitutions, deletions, truncations, and insertions. Methods for such manipulations are generally known in the art.

Methods for determining if the heterologous epitope is recognized by an HIV-1 neutralizing antibody are disclosed in U.S. Provisional Application No. 60,606,053, filed Aug. 31, 2004 and 60/562,824, filed Apr. 16, 2004 and U.S. Provisional Application No. 60/649,551, filed Feb. 3, 2005, entitled “Molecular Scaffolds for HIV-1 Epitopes,” each of these references is herein incorporated by reference. In addition, the formation of an antibody-antigen complex can be assayed using a number of well-defined diagnostic assays including conventional immunoassay formats to detect and/or quantitate antigen-specific antibodies. Such assays include, for example, enzyme immunoassays, e.g., ELISA, cell-based assays, flow cytometry, radioimmunoassays, and immunohistochemical staining. Numerous competitive and non-competitive protein binding assays are known in the art and many are commercially available. Representative assays include, for example, various binding assays with chemokine receptors (CCR5 or CXCR4), gp41, characterized domains of these polypeptides, and competitive binding assays with characterized HIV-1 binding antibodies.

In addition, if the chimeric envelope polypeptide is associated with a retrovirus, “neutralization” of the virus in the presence of an appropriate neutralizing antibody can be assayed. For example, a reduction in the establishment of HIV infection and/or reducing subsequent HIV disease progression in this sample when compared to a control sample that lacks the HIV-1 neutralizing antibody can also be monitored. A reduction in the establishment of HIV infection and/or a reduction in subsequent HIV disease progression encompass any statistically significant reduction in HIV activity in the sample. Methods to assay for the neutralization activity include, but are not limited to, a single-cycle infection assay as described in Martin et al. (2003) Nature Biotechnology 21:71-76. In this assay, the level of viral activity is measured via a selectable marker whose activity is reflective of the amount of viable virus in the sample, and the IC50 is determined. In other assays, acute infection can be monitored in the PM1 cell line or in primary cells (normal PBMC). In this assay, the level of viral activity can be monitored by determining the p24 concentrations using ELISA. See, for example, Martin et al. (2003) Nature Biotechnology 21:71-76, herein incorporated by reference. Further methods include those employing the adherent HeLa cell-derived JC53BL-13 cell line (NIH AIDS Research and Reference Reagent Program Catalogue No. 8129, TZM-b1) as described in Wei et al. (2003) Nature 422:307-312, herein incorporated by reference.

A variety of epitopes for HIV-1 neutralizing antibodies are known in the art. Such epitopes are found, for example, in gp160, gp120, or gp41. In specific embodiments, the epitope recognized by the HIV-1 neutralizing antibody is from an HIV-1 envelope polypeptide. Any HIV strain or isolate can be used. See, for example, HIV Molecular Immunology (2002) Korber et al. ed., Los Alamos National Laboratory, Theoretical Biology and Biophysics, Los Alamos, N. Mex. LA-UR 03-5816, which is herein incorporated by reference in its entirety.

In specific embodiments, the epitope recognized by the HIV-1 neutralizing antibody is in gp41. For example, epitopes found in the N-terminal hydrophobic fusion peptide of gp41 (about amino acids 512 to about 527 of SEQ ID NO: 10), the disulfide-loop region of gp41 that links the N-HR and C-HR regions (about amino acids 581 to about 628 of SEQ ID NO: 10), the N-HR region of gp41 (about amino acids 546 to about 581 of SEQ ID:10), the C-HR of gp41 (about amino acids 628 to about 661 of SEQ ID NO: 10), the membrane proximal region of gp41 (about amino acids 657 to about amino acids 684 of SEQ ID NO: 10) can be used.

As used herein, an “MPER region” comprises the MPER region found in HIV-1 YU-2 (i.e., N-LALDKWASLWNWFDITKWLWYIK-C (SEQ ID NO:38)). A functional variant of an MPER region will continue to be recognized by an HIV-1 binding antibody. Methods to assay for the binding of the HIV-1 binding antibody are discussed elsewhere herein as are methods to determine if the variant sequence is immunologically equivalent. Such variants can include internal and/or terminal additions, deletions, and/or substitutions. The variants can differ by 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or more amino acids. Variants of the MPER region are known. See, for example, FIG. 8 which provides the MPER region of HXB2C, ST, and UC1. Additional variants of the MPER region are shown in FIG. 7.

Epitopes of interest within the membrane proximal region of gp41 can be found, for example, between about amino acids 657 to 675, about amino acid 670 to 684, about amino acids 665 to about 680, or about amino acids 667 to about 681 of SEQ ID NO:10. See, Follis et al. (2002) J. of Virology 76:7356-7362 for additional domains of gp41 that are of interest. In other embodiments, an epitope of the HIV-1 neutralizing antibody is found in the bridging sheet, variable loop 1, variable loop 2, variable loop 3, variable loop 4, the chemokine receptor binding site, or the CD4 binding site. See, for example, FIG. 1 which outlines the various domains of gp120 in the HXB2 HIV-1 isolate. It is recognized that an entire domain of the HIV-1 envelope protein may be inserted into the heterologous envelope polypeptide or alternatively, any fragment of the domain from the HIV-1 envelope polypeptide can be used as the epitope for the HIV-1 binding antibody.

Additional epitopes of interest include, but are not limited to, the 4E 10 epitope (SEQ ID NO:15), the Z13 epitope (SEQ ID NO:15) and the 2F5 epitope (SEQ ID NO: 16). See, for example, U.S. Publication No. 20030157063, Muster et al. (1993) J. Virol. 67:6642-6647, Zwick et al. (2001) J. Virology 75:10892-10905, Ferrantelli et al (2002) Curr. Opin. Immunol. 14:495-502, and Wang et al. (2003) Curr. Pharm. Des. 9:1771-87. Each of these epitopes is denoted in FIG. 4. Alternatively, the entire neutralization 2F5/4E10/Z13 cluster could be employed. Accordingly, each of the epitopes or domains from HIV-1 can be engineered into the corresponding position of a non-HIV-1 envelope polypeptide. For example, amino acids 657 to 684 of SEQ ID NO: 10 can replace the corresponding amino acids (i.e., amino acids 655-682) of SEQ ID NO:2. Alternatively, amino acids 657 to 684 of SEQ ID NO:10 can replace the corresponding amino acids (i.e., amino acids 665 to 673 or amino acids 648-675) of SEQ ID NO: 14.

Additional epitopes for HIV-1 binding antibodies include the epitope located at amino acid number 662 to 667 of gp41 of the HIV-1 isolate BH10 (GenBank Acc No. M1565) with the number as described in the Swissprot database entry ENV$HIV10; the epitope located at amino acid position 79 to 184 or amino acid position 326 to 400 of the processed gp120 of HIV-1 isolate BH10 (GenBank Acc. No. M15165, with numbering as described in Swissprot database entry ENV$SHIV10). See, for example, U.S. Pat. No. 6,268,484. See, also, Rizzuto et al. (2000) AIDS Res Hum Retroviruses 16:741-749 and Xiang et al. (2002) AIDS Res Hum Retroviruses 18:1207-1217 which characterize the HIV-1 gp120 structures implicated in the CCR5 and CD4-induced antibodies. Epitopes for 17b, 48d, b12, and 2G12 are also known. See, for example, Rizzuto et al. (1998) Science 280:1949-1953, Thali et al. (1993) J. Virol. 67:3978-3988, and Trkola et al. (1996) J. Virol. 70:1100-1108. A review of additional characterized epitopes for HIV-1 binding antibodies and their location in the HIV-1 envelope polypeptide can be found in HIV Molecular Immunology (2002) Bette et al. eds., Los Alamos National Laboratory, Theoretical Biology and Biophysics, Los Alamos, N. Mex. LA-UR 03-5816. The contents of each of these references are herein incorporated by reference in their entirety.

It is further recognized that immunologically equivalent epitopes for the HIV-1 neutralizing antibodies discussed above are known and can be used in the methods and compositions of the invention. Immunologically equivalent epitopes for 2F5 are known. See, for example, U.S. Application Publication No. 20030157063, Kattinger et al. (1992) Septime Colloque des Cent Gardes, 299-303, EP-0570357, and Zwick et al. (2001) J. Virology 75:10892-10900 which disclose immunologically equivalent epitopes of the 2F5 epitope. Such immunologically equivalent epitopes, while differing in their amino acid sequence, continue to be recognized by the 2F5 monoclonal antibody (Virus Testing Systems, Houston, Tex., USA). Immunologically equivalent epitopes for 4E10 and Z13 are also known. See, for example, Zwick et al. (2001) J. Virology 75:10892-10900. Again, such immunologically equivalent epitopes, while differing in their amino acid sequence continue to be recognized by the 4E10 monoclonal antibody or the Z13 antibody. Accordingly, immunologically equivalent epitopes can differ from the epitope set forth in SEQ ID NO: 15 and 16 by at least 1, 2, 3, 4, 5, 6, 7, 8 or more amino acids. The differences can be generated by amino acid substitutions, deletions and insertions. Methods to determine if two epitopes are immunologically equivalent are known in the art. See, for example, U.S. Application Publication No. 20030157063, EP-0570357 and Zwick et al. (2001) J. Virology 75:10892-10900, all of which are herein incorporated by reference.

Exemplary chimeric polynucleotides and polypeptides of the invention include sequences encoding non-HIV-1 envelope polypeptides, or variants thereof, which have been modified to have a heterologous HIV-1 MPER region, a 4E10, a Z13, or a 2F5 epitope or a functional variant (immunologically equivalent epitope) thereof as discussed elsewhere herein. Non-limiting examples of such chimeric polynucleotides and polypeptides include the envelope polypeptide of HIV-2 7312A in which amino acids 675 and 676 (HXB-2c, SEQ ID NO:10) are altered from L to I and from A to T, respectively. As shown in FIG. 4, these positions correspond to amino acids 673 and 674 of the envelope polypeptide of HIV-2 7312A. This chimeric polypeptide comprises a heterologous epitope that renders the virus sensitive to neutralization by 4E10 antibodies. In other embodiments, the chimeric envelope polypeptide, or nucleotide sequence encoding it, comprises the HIV-2 ST envelope polypeptide in which amino acids 675 and 676 (HXB-2c, SEQ ID NO: 10) are altered from L to A and from T to A, respectively. This alteration eliminates 4E10 binding. As shown in FIG. 4, these positions correspond to amino acid 664 and 665 of the HIV-2 ST envelope polypeptide (SEQ ID NO:14).

Additional non-limiting examples include the chimeric envelope polypeptide of HIV-2 7312A or HIV-2 ST in which the heterologous 2F5 epitope, or the immunologically equivalent epitope thereof, is engineered into the polynucleotide. One such chimeric polypeptide, and the chimeric polynucleotide encoding it includes the polypeptide having site-directed mutations in the HIV-2 7312A envelope polypeptide at positions 660 (K to A), 662 (N to D), 663 (S to K), and 665 (D to A) of SEQ ID NO:2, which together make the HIV-2 sequence identical to that of the 2F5 epitope region of HIV-1 YU2. As shown in FIG. 4, these positions correspond to amino acids 662, 664, 665, and 667, respectively, of HXB-2c (SEQ ID NO:10). Additional chimeric HIV-1 envelope polypeptides having a heterologous MPER region, or a functional variant or fragment thereof, are set forth in FIG. 7.

4. Immunogenic Compositions

Immunogenic compositions of the invention can include an isolated chimeric polypeptide or active variant thereof or an isolated polynucleotide encoding the chimeric envelope polypeptide of the invention or active variant thereof. An isolated chimeric envelope polypeptide of the invention is present in an immunogenic composition in an amount sufficient to elicit an immune response against the heterologous epitope upon administration of a suitable dose to a subject. An isolated chimeric polynucleotide encoding a chimeric envelope polypeptide of the invention can also be present in the immunogenic composition in an amount sufficient such that administration of a suitable dose to a subject results in the expression of the encoded chimeric envelope polypeptide, which stimulates an immune response against the heterologous HIV-1 epitope. As used herein, a “subject” is defined as any animal including any mammal, such as, rodents, rabbits, goats, sheep, humans, primates, etc.

It is recognized that the immunogenic compositions can comprise at least two different chimeric envelope polypeptides and/or polynucleotides encoding the chimeric polynucleotides. Variations of this embodiment can provide as many different immunogenic sequences as desired, for example, 3, 4, 5, 6, 7, 8, 9, 10 or more different sequences encoding the chimeric polypeptides.

a. Immunogenic Compositions Comprising the Chimeric Envelope Polynucleotide

The invention provides immunogenic compositions comprising a chimeric envelope polypeptide of the invention or an active variant or fragment thereof. In one embodiment, an immunogenic composition of the invention includes cells expressing a chimeric envelope polypeptide of the invention, a cell lysate, or a fraction thereof, containing the chimeric polypeptide, such as, e.g., a membrane fraction. In other embodiments, the immunogenic composition comprises an isolated chimeric envelope polypeptide or variant thereof.

In other embodiments, the immunogenic chimeric envelope polypeptide or active variant thereof can be provided as a virus-derived vaccine. As used herein, the term “virus-derived vaccine” refers to a vaccine containing a viral particle, a virus-like particle (VLP), some portion of a viral particle or VLP, and/or a virally infected cell that displays the antigen on its surface, wherein administration of the particle or cell to an organism elicits an immune response to the displayed antigen.

Immunization of subjects with engineered viral-like particles and/or infected cells is well known in the art. Virus-derived vaccines can be advantageous because the viral infection component can promote a vigorous immune response that activates B lymphocytes, helper T lymphocytes, and cytotoxic T lymphocytes. Numerous viral species can be used to produce recombinant viruses useful in virus-derived vaccines. Examples include vaccinia virus (International Patent Publication WO 87/06262; Cooney et al. (1993) Proc. Natl. Acad. Sci. USA 90:1882-6; Graham et al. (1992) J. Infect. Dis. 166:244-52; McElrath et al. (1994) J Infect. Dis. 169:41-7) and canarypox virus (Pialoux et al. (1995) AIDS Res. Hum. Retroviruses 11:373-81; Andersson et al. (1996) J. Infect. Dis. 174:977-85; Fries et al. (1995) Vaccine 14:428-34; Gonczol et al. (1995) Vaccine 13:1080-5).

Virus-derived vaccines can be treated in a manner to inactivate or attenuate the virus. An attenuated recombinant virus refers to a virus that has been altered in a manner that renders the virus less virulent than the native virus. Methods for inactivating or attenuating virus are known in the art, and include, for example, treatment with paraformaldehyde, formalin, phenol, UV light, elevated temperature and the like. U.S. Pat. No. 6,503,753 describes methods for photoinactivation of HIV reverse transcriptase which thereby inactivates the HIV virus. Primate immunodeficiency viruses can also be prepared that are replication-defective. U.S. Pat. No. 6,500,623 describes HIV replication-defective viral particles and means for producing them. Other techniques for producing inactivated, attenuated and replication defective viruses are known in the art.

Virus-derived vaccines have also been prepared using defective adenovirus or adenovirus (Gilardi-Hebenstreit et al. (1990) J. Gen. Virol. 71:2425-31; Prevec et al. (1990) J. Infect. Dis. 161:27-30; Lubeck et al. (1989) Proc. Natl. Acad. Sci. USA 86:6763-7; Xiang et al. (1996) Virology 219:220-7). Other viruses that can be engineered to produce recombinant viruses useful in vaccines include retroviruses that are packaged in cells with amphotropic host range (see Miller (1990) Human Gene Ther. 1:5-14), and attenuated or defective DNA virus, such as, but not limited to, herpes simplex virus (HSV) (see, e.g., Kaplitt et al. (1991) Molec. Cell. Neurosci. 2:320-330), papillomavirus, Epstein Barr virus (EBV), adeno-associated virus (AAV) (see, e.g., Samulski et al. (1987) J. Virol. 61:3096-3101; Samulski et al. (1989) J. Virol. 63:3822-3828), poxvirus (U.S. Pat. Nos. 4,769,330, 4,722,848, 4,603,112, 5,110,587, 5,174,993, and 5,863,542), and the like.

A pharmaceutically acceptable carrier suitable for use in the invention is non-toxic to cells, tissues, or subjects at the dosages employed, and can include a buffer (such as a phosphate buffer, citrate buffer, and buffers made from other organic acids), an antioxidant (e.g., ascorbic acid), a low-molecular weight (less than about 10 residues) peptide, a polypeptide (such as serum albumin, gelatin, and an immunoglobulin), a hydrophilic polymer (such as polyvinylpyrrolidone), an amino acid (such as glycine, glutamine, asparagine, arginine, and/or lysine), a monosaccharide, a disaccharide, and/or other carbohydrates (including glucose, mannose, and dextrins), a chelating agent (e.g., ethylenediaminetetratacetic acid [EDTA]), a sugar alcohol (such as mamuitol and sorbitol), a salt-forming counterion (e.g., sodium), and/or an anionic surfactant (such as Tween™, Pluronics™, and PEG).

In one embodiment, the pharmaceutically acceptable carrier is an aqueous pH-buffered solution.

Preferred embodiments include sustained-release compositions. An exemplary sustained-release composition has a semi permeable matrix of a solid hydrophobic polymer to which the polypeptide is attached or in which the polypeptide is encapsulated. Examples of suitable polymers include a polyester, a hydrogel, a polylactide, a copolymer of L-glutamic acid and T-ethyl-L-glutamase, non-degradable ethylene-vinylacetate, a degradable lactic acid-glycolic acid copolymer, and poly-D-(−)-3-hydroxybutyric acid. Such matrices are in the form of shaped articles, such as films, or microcapsules.

Exemplary sustained release compositions include polypeptides attached, typically via ε-amino groups, to a polyalkylene glycol (e.g., polyethylene glycol [PEG]). Attachment of PEG to proteins is a well-known means of extending in vivo half-life (see, e.g., Abuchowski et al. (1977) J. Biol. Chem. 252:3582-86. Any conventional “pegylation” method can be employed, provided the “pegylated” variant retains the desired function(s).

In another embodiment, a sustained-release composition includes a liposomally entrapped polypeptide. Liposomes are small vesicles composed of various types of lipids, phospholipids, and/or surfactants. These components are typically arranged in a bilayer formation, similar to the lipid arrangement of biological membranes. Liposomes containing polypeptides are prepared by known methods, such as, for example, those described in Epstein et al. (1985) PNAS USA 82:3688-92, and Hwang et al. (1980) PNAS USA 77:4030-34.

Immunogenic compositions of the invention can be stored in any standard form, including, e.g., an aqueous solution or a lyophilized cake. Such compositions are typically sterile when administered to subjects. Sterilization of an aqueous solution is readily accomplished by filtration through a sterile filtration membrane. If the composition is stored in lyophilized form, the composition can be filtered before or after lyophilization and reconstitution.

b. Immunogenic Compositions Comprising Polynucleotides Encoding the Chimeric Envelope Polypeptides or Variants Thereof

An alternative to traditional immunization with a polypeptide antigen involves the direct in vivo introduction of a polynucleotide encoding the antigen into tissues of a subject for expression of the antigen by the cells of the subject's tissue. Polynucleotide-based compositions used to vaccinate a subject are termed “polynucleotide vaccines.” As used herein, the term “polynucleotide-vaccine” is a vaccine containing one or more polynucleotides encoding an antigen, wherein administration of the polynucleotide to an organism results in expression of the encoded antigen, followed by an immune response to that antigen. Accordingly, an immunogenic composition comprising a chimeric polynucleotide encoding a chimeric envelope polypeptide or variant thereof is provided. Such compositions can include other components including, for example, a storage solution, such as a suitable buffer, e.g., a physiological buffer. In another embodiment, the other component is a pharmaceutically acceptable carrier as described above.

The use of polynucleotide vaccines are described in Donnelly et al. (1997) Annual Review Immuno 15:617-648; Gurunathan et al. (2000) Annu. Rev. Immunol. 18:927-974; WO 95/20660; WO 93/19183; Conry et al. (1994) Cancer Res. 54:1164-1168; Cox et al. (1993) Virol 67:5664-5667; Davis et al. (1993) Hum. Mole. Genet. 2:1847-1851; Sedegah et al. Proc. Natl. Acad. Sci. 91:9866-9870; Montgomery et al. (1993) DNA Cell Bio. 12:777-783; Ulmer et al. (1993) Science 259:1745-1749; Wang et al. (1993) Proc. Natl. Acad. Sci. 90:4156-4160; and, Xiang et al. (1994) Virology 199:132-140).

In other embodiments, the composition comprising the polynucleotide encoding the chimeric envelope polypeptide further includes a component that facilitates entry of the polynucleotide into a cell. Components that facilitate intracellular delivery of polynucleotides are well-known and include, for example, lipids, liposomes, water-oil emulsions, polyethylene imines and dendrimers, any of which can be used in compositions according to the invention. Lipids are among the most widely used components of this type, and any of the available lipids or lipid formulations can be employed with the polynucleotides of the invention. Typically, cationic lipids are preferred. Preferred cationic lipids include N-[1-(2,3-dioleyloxy)propyl]--n,n,n-trimethylammonium chloride (DOTMA), dioleoyl phosphotidylethanolamine (DOPE), and/or dioleoyl phosphatidylcholine (DOPC). Polynucleotides can also be entrapped in liposomes, as described above for polypeptides.

In another embodiment, polynucleotides are complexed to dendrimers, which can be used to transfect cells. Dendrimer polycations are three dimensional, highly ordered oligomeric and/or polymeric compounds typically formed on a core molecule or designated initiator by reiterative reaction sequences adding the oligomers and/or polymers and providing an outer surface that is positively charged. Suitable dendrimers include, but are not limited to, “starburst” dendrimers and various dendrimer polycations. Methods for the preparation and use of dendrimers to introduce polynucleotides into cells in vivo are well known to those of skill in the art and described in detail, for example, in PCT/US83/02052 and U.S. Pat. Nos. 4,507,466; 4,558,120; 4,568,737; 4,587,329; 4,631,337; 4,694,064; 4,713,975; 4,737,550; 4,871,779; 4,857,599; and 5,661,025.

Accordingly, the chimeric polynucleotide of the invention can be provided in an expression cassette for expression in a cell. The cassette can include 5′ and 3′ regulatory sequences operably linked to the chimeric polynucleotide of the invention. “Operably linked” is intended to mean a functional linkage between two or more elements. For example, an operable linkage between a chimeric polynucleotide and a regulatory sequence (i.e., a promoter) is a functional link that allows for expression of the chimeric polynucleotide. Operably linked elements may be contiguous or non-contiguous. When used to refer to the joining of two protein coding regions, by operably linked is intended that the coding regions are in the same reading frame. The cassette may additionally contain at least one additional gene to be cotransformed into the cell of interest. Such an expression cassette is provided with a plurality of restriction sites and/or recombination sites for insertion of the chimeric polynucleotide to be under the transcriptional regulation of the regulatory regions. The expression cassette may additionally contain selectable marker genes.

The expression cassette will include in the 5′-3′ direction of transcription, a transcriptional and translational initiation region (i.e., a promoter), a chimeric polynucleotide of the invention, and a transcriptional and translational termination region (i.e., termination region) functional in the cell type of interest. The regulatory regions (i.e., promoters, transcriptional regulatory regions, and translational termination regions) and/or the chimeric polynucleotide of the invention may be native/analogous to the host cell or to each other. Alternatively, the regulatory regions and/or the chimeric polynucleotide of the invention may be heterologous to the host cell or to each other.

In preparing the expression cassette, the various DNA fragments may be manipulated, so as to provide for the DNA sequences in the proper orientation and, as appropriate, in the proper reading frame. Toward this end, adapters or linkers may be employed to join the DNA fragments or other manipulations may be involved to provide for convenient restriction sites, removal of superfluous DNA, removal of restriction sites, or the like. For this purpose, in vitro mutagenesis, primer repair, restriction, annealing, resubstitutions, e.g., transitions and transversions, may be involved.

As is well known in the art, a large number of factors can influence the efficiency of expression of antigen genes and/or the immunogenicity of DNA vaccines. Examples of such factors include the vector, the promoter used to drive antigen gene expression, and the stability of the inserted gene in the plasmid. Depending on their origin, promoters differ in tissue specificity and efficiency in initiating mRNA synthesis (Xiang et al. (1994) Virology 209:564-579; Chapman et al. (1991) Nucle. Acids. Res. 19:3979-3986). Many DNA vaccines in mammalian systems have relied upon viral promoters derived from cytomegalovirus (CMV).

c. Additional Components of Immunogenic Compositions

Compositions comprising the polynucleotides or polypeptides can be stored in any standard form, including, e.g., an aqueous solution or a lyophilized cake. Such compositions are typically sterile when administered to cells or subjects. Sterilization of an aqueous solution is readily accomplished by filtration through a sterile filtration membrane. If the composition is stored in lyophilized form, the composition can be filtered before or after lyophilization and reconstitution.

The various immunogenic compositions of the invention can include one or more adjuvant. The term “adjuvant” refers to a compound or mixture that enhances the immune response to an antigen. Exemplary adjuvants include, but are not limited to, complete Freund's adjuvant, incomplete Freund's adjuvant, saponin, mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil or hydrocarbon emulsions, keyhole limpet hemocyanins, dinitrophenol, and BCG (bacille Calmette-Guerin) and Corynebacterium parvum. Selection of an adjuvant depends on the subject to be vaccinated. Preferably, a pharmaceutically acceptable adjuvant is used. A preferred adjuvant for human subjects is alum (alumina gel).

Methods

The immunogenic compositions of the invention can be employed to generate antibodies that recognize the chimeric envelope polypeptide of the invention. The method comprises administering to a subject an immunogenic composition comprising a chimeric envelope polypeptide of the invention or administering to the subject a polynucleotide encoding a chimeric envelope polypeptide of the invention. As outlined in detail below, immunogenic compositions of the invention can be administered to the subject by any suitable route of administration. Accordingly, in one embodiment, an immunogenic composition is administered to a subject to generate antibodies that recognize the heterologous HIV-1 neutralizing epitope. Such antibodies find use in HIV research. Generally, the subject employed in this embodiment is one typically employed for antibody production. Mammals, such as, rodents, rabbits, goats, sheep, etc., are preferred.

The antibodies generated can be either polyclonal or monoclonal antibodies. Polyclonal antibodies are raised by injecting (e.g. subcutaneous or intramuscular injection) antigenic polypeptides into a suitable animal (e.g., a mouse or a rabbit). The antibodies are then obtained from blood samples taken from the animal. The techniques used to produce polyclonal antibodies are extensively described in the literature. Polyclonal antibodies produced by the subjects can be further purified, for example, by binding to and elution from a matrix that is bound with the polypeptide against which the antibodies were raised. Those of skill in the art will know of various standard techniques for purification and/or concentration of polyclonal, as well as monoclonal, antibodies. Monoclonal antibodies can also be generated using techniques known in the art.

In other methods, the immunogenic compositions of the invention can be used to elicit an immune response in a subject. The method comprises introducing into the subject an effective concentration of an immunogenic composition comprising a chimeric envelope polypeptide of the invention or active variant thereof. In further embodiments, the method comprises administering an immunogenic composition comprising a polynucleotide which encodes a chimeric envelope polypeptide of the invention or a variant thereof and expressing the chimeric polynucleotide in the subject.

In other methods, the immunogenic compositions of the invention can be used as vaccines. In one method, the immunogenic composition is administered to individuals who are not infected with HIV-1 to reduce the risk of, or prevent, infection (prophylaxis of HIV-1 infection). The immunogenic composition can also be administered to individuals who are already infected with HIV-1, but are still able to mount an immune response. A so-called “therapeutic vaccine” can ameliorate the existing infection (for example, by improving the subject's condition or slowing or preventing disease progression) and/or can provide prophylaxis against infection with additional HIV-1 strains. Accordingly, methods for inhibiting or preventing infection by HIV-1 in a subject are provided. This method comprises administering to the subject an effective concentration of an immunogenic composition comprising the chimeric envelope polypeptide of the invention or active variant thereof. In further embodiments, the method comprises administering an immunogenic composition comprising a polynucleotide which encodes a chimeric envelope polypeptide of the invention, and expressing the chimeric polynucleotide in the subject.

Polypeptide-based immunogenic compositions are conveniently administered by injection (e.g., subcutaneous, intradermal, intramuscular, intraperitoneal, intravenous, etc.). Alternative routes include oral administration (tablets and the like) and inhalation (e.g., using commercially available nebulizers for liquid formulations or lyophilized or aerosolized formulations). Polypeptide compositions may also be administered via microspheres, liposomes, immune-stimulating complexes (ISCOMs), or other microparticulate delivery systems or sustained release formulations introduced into suitable tissues (such as blood).

As discussed above, polynucleotide-based immunogenic compositions of the invention can be employed to express an encoded polypeptide in vivo, in a subject, thereby eliciting an immune response against the encoded polypeptide. Various methods are available for administering polynucleotides into animals. the selection of a suitable method for introducing a particular polynucleotide into an animal is within the level of skill in the art. See, for example, Zhu et al. (1993) Science 261:209-211; Ulmer et al. (1993) Science 259:1745-1749; WO 93/17706; Eisenbraun et al. (1993) DNA Cell Biol. 12: 791-797. Polynucleotides of the invention can also be introduced into a subject by other methods known in the art, e.g., transfection, electroporation, microinjection, transduction, cell fusion, DEAE dextran, calcium phosphate precipitation, lipofection (lysosome fusion), or a DNA vector transporter (see, e.g., Wu et al. (1992) J. Biol. Chem. 267:963-967; Wu and Wu (1988) J. Biol. Chem. 263:14621-14624; Canadian Patent Application No. 2,012,311).

An “effective concentration” is defined herein as an amount of a biologically active agent that produces an intended biological activity. The effective concentration of either the chimeric envelope polypeptide or the chimeric envelope polynucleotide administered in the immunogenic composition depends on the properties of the particular composition, e.g., the immunogenicity of a particular formulation, administration route, immunization regimen, condition of the subject and the like, and the determination of a suitable dose for a particular set of circumstances is within the level of skill in the art. Different dosages can be used in a series of sequential inoculations. Thus, the practitioner may administer a relatively large dose in a primary inoculation and then boost with relatively smaller doses of the chimeric envelope polypeptide.

The immune response against the heterologous epitope of the chimeric polypeptide can be generated by one or more inoculations of a subject with an immunogenic composition of the invention. A first inoculation is termed a “primary inoculation” and subsequent immunizations are termed “booster inoculations.” Booster inoculations generally enhance the immune response, and immunization regimens including at least one booster inoculation are preferred. Any type of immunogenic composition described above may be used for a primary or booster immunization. Thus, for example, an immunogenic composition comprising polynucleotides (e.g., or a virus-derived vaccine) of the invention can be used for a primary immunization, followed by boosting with an immunogenic composition containing polypeptides of the invention, or vice versa. In addition, a primary immunization and one or more booster immunization can provide the same chimeric polypeptide and/or different chimeric polypeptides.

In one embodiment, a suitable immunization regimen includes at least three separate inoculations with one or more immunogenic compositions of the invention, with a second inoculation being administered more than about two, about three to eight, or about four, weeks following the first inoculation. Generally, the third inoculation is administered several months after the second inoculation, and in specific embodiments, more than about five months after the first inoculation, more than about six months to about two years after the first inoculation, or about eight months to about one year after the first inoculation. Periodic inoculations beyond the third are also desirable to enhance the subject's “immune memory.”

The adequacy of the vaccination parameters chosen, e.g., formulation, dose, regimen and the like, can be determined by taking aliquots of serum from the subject and assaying antibody titers during the course of the immunization program. Alternatively, the T cell populations can by monitored by conventional methods. In addition, the clinical condition of the subject can be monitored for the desired effect, e.g., prevention of HIV-1 infection or progression to ASDS, improvement in disease state (e.g., reduction in viral load), or reduction in transmission frequency to an uninfected partner. If such monitoring indicates that vaccination is sub-optimal, the subject can be boosted with an additional dose of immunogenic composition, and the vaccination parameters can be modified in a fashion expected to potentiate the immune response. Thus, for example, the dose of the chimeric envelope polypeptide or polynucleotide and/or adjuvant can be increased or the route of administration can be changed.

The following examples are offered by way of illustration and not by way of limitation.

EXPERIMENTAL Example 1

HIV-1 and HIV-2 share less than 50% sequence similarity in envelope and they generally exhibit little cross-neutralization. We postulated that HIV-1 neutralizing antibody (Nab) epitopes could be identified in, or molecularly engineered into, functional HIV-2 env glycoproteins. Sequence alignments of HIV-1 and HIV-2 viruses were examined to identify conserved regions in the membrane proximal external region (MPER) of gp41 and site-directed mutagenesis was used to change selected amino acids in this region of HIV-2 to resemble HIV-1. HIV-2 virions bearing envelopes with 4E 10 core epitope amino acids, or control viruses containing wild-type HIV-1 or HIV-2 env, were analyzed for neutralization susceptibility to a panel of HIV-1 and HIV-2 monoclonal antibodies (Mab) or HIV-1 infected patient plasma using a JC53b1-13 HIV entry assay previously described (Nature 422:307, 2003).

The neutralization of HIV-2 by 4E10 and 2F5 monoclonal antibody was demonstrated. HIV-2 viruses 7312A, UC1, and ST were pre-incubated for 1 hour at 37° C. with the indicated concentrations of 4E10 and 2F5 monoclonal antibody. They were then plated on JC53b1-13 cells and infectivity determined after 48 hrs, as described in Decker et al (submitted and incorporated into this patent application). Site-directed mutations in the HIV-2 7312A envelope at positions 675 (L to I) and 676 (A to T) making the sequence of the 4E10 epitope identical to that of HIV-1 YU2 (see inset of FIG. 5) rendered the virus susceptible to 4E10; conversely, altering these same two amino acids in the 4E10 sensitive HIV-2 ST virus to alanine residues rendered this virus resistant to 4E10 (data not shown).

More specifically, virus bearing a prototypic HIV-1 env glycoprotein (YU2) was intermediately sensitive to neutralization by 4E10 (IC50=25 ug/ml), 2F5 (IC50=25 ug/ml), and b12 (IC50=3 ug/ml). Virus containing the envelope of HIV-2 strain 7312A was resistant to neutralization by all three Mabs (IC50>50 ug/ml). Site-directed substitution of amino acid 675 of SEQ ID NO: 10 (L to I) and amino acid 676 of SEQ ID NO: 10 (A to T) in the 7312A MPER (corresponding to amino acid positions 673 and 674, respectively, of SEQ ID NO:2) rendered the virus remarkably sensitive to neutralization by 4E10 (IC50=0.8 ug/ml) (See, FIG. 5) but not by 2F5 or b12. Conversely, altering these same two amino acids in the 4E10 sensitive HIV-2 ST virus to alanine residues rendered this virus resistant to 4E10 (data not shown). Two naturally-occurring strains of HIV-2 (ST and UC1) were found to be extremely sensitive to neutralization by 4E10 (IC50=0.1 and 1.2 ug/ml, respectively) but were resistant to 2F5 and b12. Twenty-four HIV-1 clade B patient plasmas were examined for 4E10-like Nabs; six showed evidence of neutralization with reciprocal IC50 titers between 0.028 and 0.001 (data not shown).

In a similar fashion, site-directed mutations in the HIV-2 7312A envelope at positions 660 (K to A), 662 (N to D), 663 (S to K), and 665(D to A) of SEQ ID NO:2, which together make the HIV-2 sequence identical to that of the 2F5 epitope region of HIV-1 YU2, rendered the modified HIV-2 virus susceptible to 2F5 with an IC50 of <0.1 ug/ml; conversely, the wild-type HIV-2 7312A envelope-containing viruses were completely resistant to 2F5 (IC50>50.0 ug/ml) (data not shown). These data show that certain naturally-occurring or genetically-modified strains of HIV-2 can be used to detect HIV neutralization by 4E10 and 4E10-like antibodies and by 2F5 and 2F5-like antibodies.

Conclusions. Naturally occurring or genetically engineered variants of HIV-2 env glycoprotein can be used to detect and quantify HIV-1 elicited 4E10-like and 2F5 Nabs with great sensitivity (IC50=0.1 ug/ml) and specificity. We have evidence that an analogous approach is feasible for detecting HIV-1 elicited Nabs against other MPER epitopes as well as epitopes on gp120.

All publications and patent applications mentioned in the specification are indicative of the level of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims. 

That which is claimed:
 1. An immunogenic composition comprising a chimeric polypeptide, wherein said chimeric polypeptide comprises: a) an amino acid sequence encoding an HIV-2 envelope polypeptide, a functional variant of the HIV-2 envelope polypeptide, a Simian Immunodeficiency virus (SIV) envelope polypeptide, or a functional variant of the SIV envelope polypeptide; and b) a heterologous epitope selected from the group consisting of: i) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:38, or a functional variant thereof, wherein the amino acid sequence of said functional variant differs from SEQ ID NO:38 by up to three amino acids; ii) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:15, or an immunologically equivalent epitope thereof, wherein the amino acid sequence of said immunologically equivalent epitope differs from SEQ ID NO:15 by one amino acid; and iii) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:16, or an immunologically equivalent epitope thereof, wherein the amino acid sequence of said immunologically equivalent epitope differs from SEQ ID NO:16 by up to two amino acids; wherein said heterologous epitope is recognized by an HIV-1 neutralizing antibody, and wherein said heterologous epitope is located at a position within said amino acid sequence of a).
 2. An immunogenic composition comprising a chimeric polynucleotide, wherein said chimeric polynucleotide comprises: a) a nucleotide sequence encoding an HIV-2 envelope polypeptide, a functional variant of the HIV-2 envelope polypeptide, a Simian Immunodeficiency virus (SIV) envelope polypeptide, or a functional variant of the SIV envelope polypeptide; and b) a nucleotide sequence encoding an amino acid sequence comprising a heterologous epitope, wherein said heterologous epitope is selected from the group consisting of: i) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:38, or a functional variant thereof, wherein the amino acid sequence of said functional variant differs from SEQ ID NO:38 by up to three amino acids; ii) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:15, or an immunologically equivalent epitope thereof, wherein the amino acid sequence of said immunologically equivalent epitope differs from SEQ ID NO:15 by one amino acid; and iii) a heterologous epitope comprising the amino acid sequence set forth in SEQ ID NO:16, or an immunologically equivalent epitope thereof, wherein the amino acid sequence of said immunologically equivalent epitope differs from SEQ ID NO:16 by up to two amino acids; wherein said heterologous epitope is recognized by an HIV-1 neutralizing antibody, and wherein said nucleotide sequence of b) is located at a position within said nucleotide sequence of a).
 3. The immunogenic composition of claim 1, wherein said chimeric polypeptide is displayed on a virus, a viral-like particle or is displayed on a virally infected cell.
 4. The immunogenic composition of claim 3, wherein said viral-like particle comprises an inactivated, an attenuated, or a replication-defective viral-like particle.
 5. The immunogenic composition of claim 1, wherein said composition further comprises a pharmaceutically acceptable carrier, diluent, or adjuvant.
 6. A method of eliciting an immune response in a subject comprising: Administering to the subject an effective concentration of an immunogenic composition of claim 1; and thereby eliciting the immune response in said subject.
 7. The method of claim 6, wherein said epitope is from gp41 or gp120.
 8. The method of claim 6, wherein said epitope comprises the membrane proximal external region or a functional variant thereof.
 9. The method of claim 7, wherein said epitope comprises a 4E10 epitope, a Z13 epitope, or a 2F5 epitope.
 10. The method of claim 6, wherein said epitope is from the variable loop region of gp120.
 11. The method of claim 6, wherein said chimeric polypeptide is displayed on a virus, a viral-like particle or is displayed on a virally infected cell.
 12. The method of claim 11, wherein said viral-like particle comprises an inactivated, an attenuated, or a replication-defective viral-like particle.
 13. The method of claim 6, wherein said immunogenic composition is administered with a pharmaceutically acceptable carrier or diluent.
 14. The method of claim 6, wherein said immunogenic composition is administered with one or more adjuvant.
 15. The method of claim 6, wherein said immunogenic composition is administered subcutaneously, intraperitoneally, intramuscularly, orally, or via nasal administration.
 16. The method of claim 6, wherein said heterologous epitope is from an HIV-1 envelope polypeptide.
 17. The immunogenic composition of claim 1, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:38.
 18. The immunogenic composition of claim 1, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:15.
 19. The immunogenic composition of claim 1, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:16.
 20. The immunogenic composition of claim 2, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:38.
 21. The immunogenic composition of claim 2, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:15.
 22. The immunogenic composition of claim 2, wherein said heterologous epitope comprises the amino acid sequence set forth in SEQ ID NO:16.
 23. A method of eliciting an immune response in a subject comprising: administering to the subject an effective concentration of an immunogenic composition of claim 2; and thereby eliciting the immune response in said subject.
 24. The method of claim 23, wherein said immunogenic composition is administered with a pharmaceutically acceptable carrier or diluent.
 25. The method of claim 23, wherein said immunogenic composition is administered with one or more adjuvant.
 26. The method of claim 23, wherein said immunogenic composition is administered subcutaneously, intraperitoneally, intramuscularly, orally, or via nasal administration. 